Peroxy acid compounds have been used for cleaning or sanitizing processes. The peroxy acids have been produced in large quantities and then shipped to the use site in either dilute or concentrated form. Neither of these options is particularly desirable. Shipping dilute solutions of peroxy acids i.e., about 5% peroxy acid in water, increases shipping costs due to the dilute nature of the product, while shipping more concentrated peroxy acids is a potentially hazardous process as peroxy acids can be explosive.
The peroxy acid compositions have been stabilized with known additives for long term storage. Bowing et al, U.S. Pat. No. 4,051,058 teach peroxy containing concentrates stabilized by an organic phosphonic acid compound which sequesters bivalent metal ions. Also, Crommelynck et al, U.S. Pat. No. 4,297,298 discloses the preparation of a stable, dilute solution of peracetic acid using a strong mineral acid catalyst which is stabilized by dipicolinic acid and 2,6-pyridinedicarboxylic acid.
To avoid the hazards of shipping concentrated peroxy acid solutions, higher costs of shipping dilute solutions and problems with storage stability of concentrated solutions, processes for the point-of-use production and dosing of peroxy acids have been proposed. For example, German Patent Application No. DE-36 38 552 teaches generally the point-of-use batch preparation of a peroxy acid by reacting hydrogen peroxide, with a carboxylic acid in the presence of a mineral acid catalyst. These processes have inherent problems associated with the use of a mineral acid catalyst. Strong liquid mineral acids must be handled with the ever-present danger of spills and associated hazards for operators. Additionally, in mineral acid catalyzed point-of-use systems, the product is rather the product stream, therefore, the catalyst is essentially consumed in that it must be continuously replaced. Finally, mineral acid based point-of-use units are generally larger and more costly than resin acid based units requiring the use of more corrosion resistant materials. In contrast, resin acid catalysts may last for several months resulting in a more economical operation.
The use of a cation exchange resin to catalyze the hydrogen peroxide-carboxylic acid reaction has been discussed in the art. U.K. Patent No. 776,758 to duPont discloses the use of cation exchange resins in the preparation of peroxycarboxylic acids from the corresponding carboxylic acid and hydrogen peroxide. This reference apparently did not recognize the problems of resin catalyst swelling. U.S. Pat. No. 4,647,578 to Eckwert et al teaches the epoxidation of hydrocarbons with peroxyacetic acid using a resin catalyst. Included in this disclosure is the generation of peroxyacetic acids in a cation exchange resin. This reference suggests that hydrogen peroxide causes swelling and dissolution of the resin catalyst. Agnihotri et al, "Preparation of Peracetic Acid by Using Various Catalyst Systems", 18 Colourage No. 26, page 30 (1971) compares the reaction conversion of mineral acids including sulfuric and phosphoric acids with that using a cation exchange resin at comparable levels of hydrogen ion equivalents. This reference indicates that mineral acids achieve greater conversion than acid resins in the catalysis of the hydrogen peroxide-carboxylic acid reaction.
The prior art taken together suggests that the use of acid resins to catalyze the reaction of hydrogen peroxide and carboxylic acid to produce peroxy acids can cause several problems. First, the hydrogen peroxide can cause swelling and degradation of the acid resin catalyst. Second, the apparent slow rate at which the reaction proceeds using an acid resin can cause a production slowdown or increased costs.
A need exists for a convenient point-of-use process to produce peroxy acid compositions. Preferably, these compositions are free of strong mineral acid catalyst, and the reaction proceeds at rates comparable to or exceeding those obtained using mineral acids. A further need exists for a heterogeneous process of producing peroxy acid compounds which reduces the degradation of catalyst resins.